Vehicle controller and method of controlling a vehicle

ABSTRACT

An electric motor control unit for controlling the operation of an electric motor. The unit comprises: an electric motor controller comprising a processor having at least one input and at least one output, wherein an output of the processor is coupled to a power provider for controlling power to an electric motor; a tilt accelerometer for determining a measure of the tilt of the electric motor unit relative to a reference orientation, wherein the tilt accelerometer system comprises an output for providing a signal based on the determined measure of the tilt; wherein the output of the tilt accelerometer system is coupled to an input of the processor of the electric motor controller; wherein the power provider comprises a power output for controlling the operation of an electric motor based on the output of the tilt accelerometer system.

The present disclosure relates to electric motor controllers and to thecontrol of vehicles, and more particularly to safety control of loadlifting vehicles.

Vehicles having aerial work platforms, such a “cherry-pickers” andmaterials handling vehicles, such as fork lift trucks are used to liftand to carry loads. To avoid the vehicles tipping over it has beenproposed to limit the maximum speed of such vehicles when the vehicle isturning. In addition, tilt switches may be used to identify a loss ofstability of the vehicle. Such switches may also be used to stop thevehicle from being driven, or lifting loads when the vehicle is tiltedor tilting.

Aspects and examples of the present disclosure address related technicalproblems.

In one aspect there is provided an apparatus for controlling operationof a load bearing vehicle. The apparatus comprises: a turning input forobtaining an indication of the turning of the vehicle with respect toits direction of travel; a speed input for obtaining the linear speed ofthe vehicle in the direction of travel; an acceleration input forobtaining an accelerometer signal; and a controller configured todetermine the tilt angle of the vehicle based on the turning, the linearspeed, and the accelerometer signal, and to modify operation of thevehicle based on the tilt angle. The accelerometer signal may provide anindication of the direction of gravity to enable tilt angle to bemeasured with respect to the direction of gravity, for example theaccelerometer input may receive a measure of acceleration from amicro-electromechanical MEMS tilt accelerometer. As will be appreciated,the term “linear speed” does not imply that the vehicle is travelling isa straight line, but may refer to the instantaneous speed as a vehicleis cornering. As an example, the liner speed may be determined by thewheel rotation rate.

The vehicle may comprise a vehicle having a load bearing lift, operableto lift a load to a selected height which may be above the unloadedcentre of gravity of the vehicle. For example, the vehicle may comprisea material handling vehicle such as a fork lift truck, or an aerial workplatform such as a cherry picker. The load may comprise a person.

By knowing the angle that a vehicle is at and in some cases additionalinformation about the weight, height and/or lateral position of the loadwith respect to the vehicle, operation of the vehicle can be modified toassist safety, for example to provide a warning signal to an operator ofthe vehicle, or to limit the speed of the vehicle or operation of thelift.

A MEMs accelerometer can be used to determine acceleration as a 3Dvector, e.g. with respect to three (3) mutually perpendicular axes. Thisenables a determination of the direction in which gravity is acting withrespect to the vehicle and hence the angle or tilt of the vehicle.

Another aspect provides an electric motor control unit for controllingthe operation of an electric motor, the unit comprising: an electricmotor controller comprising a processor having at least one input and atleast one output, wherein an output of the processor is coupled to apower provider for providing power to an electric motor; a tiltaccelerometer system comprising a tilt accelerometer for determining ameasure of the tilt of the electric motor control unit relative to areference orientation, wherein the tilt accelerometer system comprisesan output for providing a signal based on the determined measure of thetilt; wherein the output of the tilt accelerometer system is coupled toan input of the processor of the electric motor controller; and whereinthe power provider comprises a power output for controlling theoperation of an electric motor based on the output of the tiltaccelerometer system. The power provider may be an inverter, or a powerstage for an electric motor.

Providing a tilt accelerometer system in an electric motor control unittogether with the electric motor controller can enable the electricmotor controller to take into account quickly and reliably the tiltangle of the control unit in order to control operation of the motor. Inparticular, with the tilt accelerometer provided in the electric motorcontrol unit, the orientation of the tilt accelerometer relative to theunit is fixed and known. This can make calibration of the tiltaccelerometer more straightforward and more accurate and hence can makecompensation for tilting accurate and reliable. The provision of anelectric motor control unit can also simplify the fitting of thecomponents to a vehicle and ensure that the output of the tiltaccelerometer is correctly coupled to the electric motor controller.

According to another aspect, there is provided a method of controllingthe operation of an electric motor for a vehicle, the method comprising:coupling to the vehicle in a fixed orientation an electric motor controlunit, the electric motor control unit comprising an electric motorcontroller and a tilt accelerometer system, the tilt accelerometersystem comprising a tilt accelerometer; coupling an output of theelectric motor controller to a control input of the electric motor tocontrol the operation of the electric motor; and calibrating the tiltaccelerometer to define the direction of a gravitational force acting onthe tilt accelerometer relative to the fixed orientation of the electricmotor control unit.

Hence the method may enable control of an electric motor for a vehicleto be adjusted based on a measure of the tilt of the control unit, whichis coupled to the vehicle. Calibration of the unit after it is fixed tothe vehicle enables the unit to be fixed to the vehicle in anyconvenient orientation before a “zero” orientation is defined.

In some possibilities, a reference orientation is determined bycalibration of the tilt accelerometer when the electric motor controlunit is secured in a fixed position relative to the vehicle, and in somecases when it is in a fixed position relative to the electric motor.

Embodiments of the invention will now be described, by way of exampleonly, with reference to the accompanying drawings in which:

FIG. 1 shows a schematic view of a control system for a vehicle;

FIG. 2 shows a schematic view of a controller for use in systems such asthat illustrated in FIG. 1; and

FIG. 3 shows a very schematic illustration of one method of operation ofthe apparatus and vehicles described with reference to FIG. 1 and FIG.2;

FIG. 4A is a schematic diagram of an electric motor control unitaccording to one embodiment;

FIG. 4B is a schematic diagram of a tilt accelerometer system accordingto one embodiment.

Embodiments of an electric motor control unit will first be describedwith reference to FIGS. 4A and 4B. The use of such a control unit onvehicles, in particular load-bearing vehicles such as aerial workplatforms and fork lift trucks, will then be described.

As illustrated schematically in FIG. 4A, an electric motor control unit400 may include, in one embodiment, a power provider 414 for providingpower to an electric motor 416. The type of power provider 414 used willdepend on the motor that is being controlled, but for example, aninverter such as a 3 phase power inverter could be used. The powerinverter 414 is controlled by a processor 412, which defines the powerlevel and phase settings for the power inverter 414 output and causesthis to vary over time as defined by control inputs 418 and a tiltaccelerometer system 410 as described below.

The control inputs 418 can include inputs from a human operator, such asa driver of a vehicle to which the control unit 400 is attached. Thecontrol inputs may also include inputs from a computer or other machineif the electric motor is driven by computer software or as part of acomputer-implemented process such as a manufacturing, warehousing ordistribution system.

A tilt accelerometer system 410 also provides an input to the processor412 to enable adjustment of the operation of the power provider 414 (andso the external electric motor 416) based on a measure of tilt of theunit.

As illustrated in FIG. 4A, the tilt accelerometer system 410, processor412 and power provider 414 are implemented as a single unit within acommon housing. The three components are electrically and electronicallycoupled and preferably share a common power source. Preferably, elementsof the three components are implemented on a single printed circuitboard, PCB. Hence the electric motor control unit 400 is provided as asingle coherent unit for attachment to an external electric motor 416and for coupling to control inputs 418 in a system.

An embodiment of the tilt accelerometer system 410 will now be describedin more detail with reference to FIG. 4B. An exemplary tiltaccelerometer system includes a tilt accelerometer 450, which optionallycomprises a MicroElectroMechanical System (MEMS) accelerometer. As setout below in more detail, the tilt accelerometer is preferably a 3 axisaccelerometer, providing an output indicating acceleration in 3dimensions. However, other types of accelerometer, in particular 2 axisaccelerometers may be sufficient for some implementations. A motioncompensation system is also provided 452 which compensates for motion ofthe electric motor control unit 400, including motion due to linearspeed in the direction of travel, and optionally acceleration in alinear direction, and acceleration due to a change in direction of thecontrol unit. This compensation is described in more detail below.

The outputs from the tilt accelerometer 450 and the motion compensationsystem 452 are provided to a tilt angle determiner 454, which adjuststhe measure of tilt output by the system to accommodate for motion ofthe electric motor control unit. The adjusted tilt angle is output fromthe tilt angle determiner 454 and provided as an input to the processor412 of the electric motor control unit 400 to adjust the operation ofthe power provider 414 as described above.

Although FIGS. 4A and 4B are illustrated as block diagrams, thefunctionality of each of the elements described in these drawings neednot be provided by a single element. For example, the functionality ofone or more of these elements may be shared with other elements, ordistributed throughout the apparatus. For example, the tilt angledeterminer 454 may be implemented as part of the processor 412 of theelectric motor control unit 400, which may then take inputs directlyfrom the tilt accelerometer 450 and the motion compensation system 452.Accordingly, it will be understood that these diagrams should not betaken to imply a necessary physical or functional separation between theelements shown in the drawings.

Use of electric motor control units as described above will now bediscussed with particular reference to load-bearing vehicles such asaerial work platforms and fork lift trucks. However, it will beappreciated the electric motor control units described herein may becoupled to any electric motor where it is desirable to control theoperation of the electric motor based on a measure of tilt. Inparticular, a unit may be coupled to an electric motor for any type ofvehicle, such as a car, van or public service vehicle. In suchsituations, the electric motor control unit may be incorporated forexample into a safety system to control operation of the vehicle whentilt is detected. Aspects and preferred features of the system describedbelow in relation to load-bearing vehicles may be applied independentlyto the electric motor control unit and tilt accelerometer systemsdescribed above.

Vehicles such as aerial work platforms, and fork lift trucks compriseload bearing lifts which may be used to lift loads to a heightsufficient to unbalance the vehicle, or to cause it to tilt or tip over.For example, they may be able to lift a load that is sufficient to movethe centre of gravity of the loaded vehicle to a position that does notlie vertically above the footprint of the wheelbase. This would beenough to tip even a stationary vehicle, but in less extreme examples,the lifted load may destabilise the vehicle and cause it to be at riskof tipping during use.

FIG. 1 illustrates a control system for use in a vehicle such as forklift trucks and aerial work platforms or cherry pickers.

The system of FIG. 1 comprises an accelerometer 10 coupled to a tiltdeterminer 12. The tilt angle determiner is coupled to a controller 14.Driver controls 16 comprise an input interface for receiving commandsfrom an operator of the vehicle, and are also coupled to the controller14. The controller 14 is coupled to a driver display 18 for providingoutput to an operator of the vehicle, a lift controller 20, forcontrolling a load bearing lift, and a traction controller 22 for movingthe vehicle.

The accelerometer 10 comprises a 3-axis accelerometer operable tomeasure the orientation of the accelerometer with respect to thedirection of gravity in 3 dimensions. The controller 14 is operable tocontrol the lift control 20 for controlling the lifting of loads, and tocontrol the traction control 22, to control the speed of the vehicle.The driver control 16 is operable to communicate input received from anoperator to the controller 14 to enable the operator to control the lift20 and to drive the vehicle.

The tilt determiner 12 is operable to obtain an indication of the linearspeed of the vehicle and the direction in which the vehicle is beingdriven with respect to its linear speed from the controller 14. The tiltdeterminer 12 is further operable to adjust the measurements obtainedfrom the accelerometer 10 based on the linear speed, and the directionin which the vehicle is being steered with respect to its direction oftravel.

In operation, with the vehicle in motion, the tilt determiner 12 obtainsa signal indicating the vehicle's linear speed and a signal indicatingthe direction in which the vehicle is being steered from the controller14. The tilt determiner also obtains an acceleration signal from theaccelerometer 10. Based on the direction in which the vehicle is beingsteered with respect to its direction of travel, the tilt determiner 12infers a radius of the turning circle of the vehicle, and determines acentripetal acceleration based on the radius of the turning circle, andthe linear speed. The tilt angle determiner uses this centripetalacceleration to modify the direction of the acceleration measured by thetilt accelerometer 10 to correct the accelerometer measurement tocompensate for vehicle motion.

FIG. 2 shows a three axis accelerometer 110, and a vehicle motioncompensator 120 coupled to another tilt angle determiner 140.

The three axis accelerometer 110 is operable to provide a threedimensional acceleration signal comprising three components ofacceleration Ax, Ay, Az, to the tilt angle determiner 140.

The vehicle motion compensator 120 is operable to obtain a speed signalindicating the linear speed of the vehicle and a steer angle signalindicating the angle at which the vehicle is steered with respect to itsdirection of travel. Based on the speed signal and the steer angle ofthe vehicle, the vehicle motion compensator is operable to determine theacceleration associated with the motion of the vehicle, e.g. the vehicleaccelerating linearly, or the vehicle being steered through a turn.Accordingly, the vehicle motion compensator 120 is operable to provide athree component signal (e.g. a three dimensional vector) representingthe acceleration associated with motion of the vehicle to the tilt angledeterminer.

The tilt angle determiner 140 is configured to modify the accelerationmeasurement A_(x), A_(y), A_(z), provided by the three axisaccelerometer by subtracting the acceleration associated with motion ofthe vehicle a_(x), a_(y), a_(z) to provide a corrected tilt anglemeasurement.

In operation, the three axis accelerometer provides a 3D accelerationsignal to the tilt calculator 140, and the vehicle motion compensatorprovides a signal representing the acceleration associated with themotion of the vehicle. The tilt angle determiner 140 then corrects the3D acceleration signal measured by the accelerometer based on thevehicle motion acceleration.

As one example, when the vehicle is vertically upright, and at rest (ormoving at constant speed in a straight line), the signal from the threeaxis accelerometer indicates a vertical acceleration corresponding tothe direction in which gravity is acting. In addition, under theseconditions the acceleration associated with motion of the vehicle iszero, so the vehicle motion compensator provides a zero output to thetilt angle determiner.

As another example, when the vehicle is vertically upright, andtravelling in a straight line but increasing its linear speed, thesignal from the three axis accelerometer indicates a verticalacceleration corresponding to the direction in which gravity is actingmodified by the linear acceleration of the vehicle. The vehicle motioncompensator 120 determines a signal indicating the linear accelerationbased on its rate of change of linear speed, and provides this signala_(x), a_(y), a_(z), to the tilt angle determiner 140. The tilt angledeterminer 140 then corrects the signal from the accelerometer A_(x),A_(y), A_(z) based on the signal a_(x), a_(y), a_(z) from the motioncompensator, and determines a tilt angle signal based on the correctedsignal from the accelerometer (which indicates the direction in whichgravity is acting).

Although FIG. 1 and FIG. 2 are illustrated as block diagrams, thefunctionality of each of the elements described in these drawings neednot be provided by a single element. For example, the functionality ofone or more of these elements may be shared with other elements, ordistributed throughout the apparatus. As another example, the example ofFIG. 1 shows a system in which a controller 14 communicates with vehiclesystems such as the traction control 22, and driver control inputs 16 toobtain indications of the linear speed and steering angle of thevehicle. Accordingly, the controller 14 of FIG. 1 can incorporate thefunctionality of the motion compensator 120 shown in FIG. 2. Inaddition, in the apparatus shown in FIG. 1, a motion compensator 140,such as that shown and described with reference to FIG. 2 may beprovided and coupled to the tilt angle determiner 12, so that thevehicle controller 14 need not perform any of the motion compensationfunctions. Accordingly, it will be understood that these diagrams shouldnot be taken to imply a necessary physical or functional separationbetween the elements shown in the drawings.

The functionality of the elements of FIGS. 1, 4A and 4B may be providedby analogue or digital components, or mixtures thereof. In some examplesthe functionality may comprise digital logic, such as combinations oflogic gates, field programmable gate arrays, FPGA, application specificintegrated circuits, ASIC, a digital signal processor, DSP, or bysoftware loaded into a programmable processor.

The accelerometers 10, 110, 450 have been described as 3 axisaccelerometers, but in some examples two axis accelerometers, or one ormore single axis accelerometers may be used. The accelerometers may bemicro-electromechanical MEMs accelerometers; however any appropriateaccelerometer may be used.

FIG. 3 illustrates one a method of operation of the apparatus shown inFIGS. 1, 2, 4A and 4B.

In the method shown in FIG. 3, a turning parameter is obtained 302indicating the turning of the vehicle with respect to its direction oftravel. The linear speed in the direction of travel is obtained 304, andoptionally the rate of change of linear speed is determined. Anaccelerometer measurement is then obtained 306 indicating the directionin which gravity is acting with respect to the accelerometer.

The accelerometer measurement is the modified 308 based on the turningparameter, the vehicle's linear speed (and optionally any change in thatspeed), and the accelerometer measurement, to determine the tilt angleof the vehicle. It is then determined 310 whether the vehicle's tiltangle is within safe limits, and in the event that the vehicle tiltangle is within safe limits, the vehicle is allowed to continue tooperate normally. In the event that it is determined that the vehiclesoperation is not within safe limits, operation of the vehicle ismodified based on the determined tilt angle.

To determine whether the vehicle is operating within safe limits, theweight of a lifted load may be taken into account, and the height towhich the load is lifter may also be taken into account. For example,the vehicle controller (e.g. controller 14 in FIG. 1) may be configuredto determine the position of the center of gravity of the vehicle basedon the vehicle's unloaded weight, the weight of the lifted load, and theheight to which it has been lifted. In some possibilities, additionalsensors on the vehicle may be used to determine the weight of the loadand the position of the load. These sensed parameters may be passed tothe vehicle controller for example using a CANBUS interface or othercommunication systems such as a wireless interface or a wiring loom.

The controller may be configured to modify the range of tilt angleswhich are defined to be safe based on the position of the loadedvehicle's center of gravity, and stored data indicating the size of thevehicle's footprint. Accordingly, the controller may permit operation ofthe vehicle at a wider range of tilt angles when the loaded center ofgravity of the vehicle is lower in height, but apply a more restrictivelimit to the tilt angles when the vehicles center of gravity ishigher—for example when a heavy load has been lifted.

To modify operation of the vehicle, an audible or visual alert may beprovided to the vehicle's operator, or the vehicle's speed may belimited or reduced. Other modifications of the vehicles operation may beapplied, such as preventing lifting to a greater height or moving theload further from the centre of gravity

It may in some examples be advantageous to calibrate the accelerometer10, 110, when the apparatus of FIGS. 2 and 3 is assembled to a vehicle.To calibrate the accelerometer, it can be positioned on the vehicle whenthe vehicle is stationary in a vertically upright position. Theapparatus can then be fixed to the vehicle whilst the vehicle isvertical, and determining the acceleration measured by the accelerometerwhen the vehicle is in this position may enable the controller of theapparatus to be configured to identify when the vehicle is verticallyupright.

Amongst the technical problems addressed by aspects of the disclosurecould be the provision of efficient data exchange between a tilt sensorand the vehicle traction and/or lift control. In addition, aspects ofthe disclosure have the advantage that the orientation of the tiltsensor is protected by the orientation of the motor controller therebyreducing the likelihood that the orientation of the tilt sensor caninadvertently be modified.

In some embodiments the motor controller may be integrated with anelectric motor into a single unit.

The foregoing examples explain some ways to put the present disclosureinto effect, other variations and modifications may be applied, and inparticular the functions described above with reference to apparatus maybe combined with any method described herein. Equally, the methodsdescribed herein may be implemented in apparatus configured to provideequivalent functionality. Other examples and variations will be apparentto the skilled addressee in the context of the present disclosure.

1. An electric motor control unit for controlling the operation of anelectric motor, the unit comprising: an electric motor controllercomprising a processor having at least one input and at least oneoutput, wherein an output of the processor is coupled to a powerprovider for controlling power to an electric motor; a tiltaccelerometer system comprising a tilt accelerometer for determining ameasure of the tilt of the electric motor control unit relative to areference orientation, wherein the tilt accelerometer system comprisesan output for providing a signal based on the determined measure of thetilt; wherein the output of the tilt accelerometer system is coupled toan input of the processor of the electric motor controller; wherein thepower provider comprises a power output for controlling the operation ofan electric motor based on the output of the tilt accelerometer system.2. The electric motor control unit according to claim 1 furthercomprising a housing containing the electric motor controller and thetilt accelerometer system.
 3. The electric motor control unit accordingto claim 1 wherein the tilt accelerometer comprises aMicroElectroMechanical System, MEMS, accelerometer.
 4. The electricmotor control unit according to claim 1 wherein the power providercomprises one of a chopper, converter or inverter.
 5. The electric motorcontrol unit according to claim 1 wherein the reference orientation isdetermined by calibration of the tilt accelerometer when the electricmotor control unit is secured in a fixed position relative to theelectric motor and/or in a fixed position with respect to a vehicle. 6.The electric motor control unit according to claim 1 further comprisingmeans for securing the electric motor control unit to a vehicle in afixed orientation relative to the vehicle.
 7. The electric motor controlunit according to claim 1 wherein the vehicle comprises a load-bearingvehicle including a load bearing lift operable to lift a load, such as aperson, to a selected height.
 8. The electric motor control unitaccording to claim 1 wherein the tilt accelerometer system comprises amotion compensation system for adjusting the output of the tiltaccelerometer based on motion of the electric motor control unit.
 9. Theelectric motor control unit according to claim 8 wherein the motioncompensation system compensates for the linear speed of the electricmotor control unit in the direction of travel.
 10. The electric motorcontrol unit according to claim 8 wherein the motion compensation systemcompensates for a turning parameter of the electric motor control unitindicating a change in its direction of travel. 11-18. (canceled)
 19. Anapparatus for controlling operation of a load bearing vehicle, whereinthe vehicle comprises a load bearing lift operable to lift a load to aselected height, wherein the apparatus comprises: a turning input forobtaining a turning parameter of the vehicle indicating a change in itsdirection of travel; a speed input for obtaining the linear speed of thevehicle in the direction of travel; an accelerometer input for obtainingan accelerometer signal; a tilt angle determiner configured to determinethe tilt angle of the vehicle based on the turning parameter, the linearspeed, and the accelerometer signal; and a controller for modifyingoperation of the vehicle based on the determined tilt angle.
 20. Theapparatus of claim 19 in which the tilt angle determiner is configuredto modify operation of the vehicle based on the tilt angle of thevehicle and at least one parameter related to the load bearing lift. 21.The apparatus of claim 20 in which the at least one parameter isselected from the list comprising: the weight of the load, the height towhich the load has been lifted, the unloaded weight of the vehicle, andthe position of the centre of gravity of the loaded vehicle.
 22. Theapparatus of claim 19 in which the tilt angle determiner is configuredto modify operation of the vehicle if the tilt angle exceeds apredetermined threshold.
 23. The apparatus of claim 22 wherein thepredetermined threshold is adjustable based on at least one of: theweight of the load on the vehicle the height of the load bearing liftthe linear speed of the vehicle in the direction of travel; and theturning parameter of the vehicle.
 24. The apparatus of claim 19 in whichmodifying operation of the vehicle comprises providing an audible orvisible signal to an operator of the vehicle.
 25. The apparatus of claim19 in which modifying operation of the vehicle comprises limiting thelinear speed at which the vehicle may be driven.
 26. The apparatus ofclaim 25 wherein the controller is configured to select a speed limitbased on the tilt angle of the vehicle and at least one parameterrelated to the load bearing lift.
 27. The apparatus of claim 19 in whichmodifying operation of the vehicle comprises limiting the height towhich the load bearing lift may lift a load, or limiting the lateraldistance by which a load may be extended from the vehicle.
 28. Theapparatus of claim 27 wherein the controller is configured to select theheight limit based on the tilt angle of the vehicle and the linear speedof the vehicle.
 29. The apparatus of claim 19 comprising an electricmotor controller for controlling an electric motor associated with atleast one of moving the vehicle, and lifting the load.
 30. The apparatusof claim 19 further comprising at least one of the vehicle and the loadbearing lift. 31-52. (canceled)